Automated tooth shade analysis and matching system

ABSTRACT

A patient&#39;s dental prosthesis (e.g. a prosthesis tooth, crown, veneer, or bridge) is made by acquiring an image of the patient&#39;s teeth that contain black and white normalization references. These references are black and white porcelain, for example, that allow software of the invention to determine absolute black and absolute white within the color image. The acquired color image is then normalized in accordance with the normalization references, which corrects the image for variations in lighting conditions and image source. The normalized image is then standardized by matching the pixels of the normalized image to selected shade standards. The dental prosthesis can then be manufactured by a lab technician by referring to the standardized image. The tooth shade analysis and matching system is also applicable to direct restorations of natural teeth, such as repair of chipped or broken teeth. Methods of whitening teeth are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is continuation of Ser. No. 09/715,273, filedNov. 17, 2000, pending, which is a divisional of Ser. No. 09/234,585,filed Jan. 21, 1999, now U.S. Pat. No. 6,190,170 B1, which claims thebenefit of U.S. Provisional Application No. 60/084,354, filed May 5,1998.

COPYRIGHT NOTICE

[0002] A portion of the disclosure of this patent document containsmaterial that is subject to copyright protection. The copyright ownerhas no objection to the facsimile reproduction by anyone of the patentdocument or the patent disclosure, as it appears in the Patent andTrademark Office patent file or records, but otherwise reserves allcopyright rights whatsoever.

FIELD OF THE INVENTION

[0003] This invention relates in general to systems for color matchingand, more specifically, to systems for analyzing and matching toothshades. Such systems are of particular use in manufacturing dentalprosthetics (e.g., crowns, bridges, veneers, and prosthetic teeth) torepair, replace or alter natural teeth, in various dental and toothwhitening procedures and to enable communication between patient,dentist and lab technician concerning such procedures.

BACKGROUND OF THE INVENTION

[0004] Dentists often repair or replace a diseased, damaged, orunsightly natural tooth of a patient with a crown, bridge, veneer, orprosthetic tooth. One obvious goal in performing such a repair orreplacement is to provide the patient with a natural-looking smiledespite the presence of the prosthesis. Attempts to reach this goalgenerally involve matching the color of the prosthesis to the color ofthe natural tooth being repaired or replaced, and to the colors of thenatural teeth that are adjacent where the prosthesis will be placed.

[0005] Similarly, dentists often perform various tooth whiteningprocedures on a patient's natural teeth to reverse the effects of aging,coffee drinking, smoking, and similar activities on the patient's dentalappearance. The goal in such procedures is also to provide the patientwith a natural-looking smile, and attempts to reach this goal alsogenerally involve color matching.

[0006] To this end, manufacturers of the various colored porcelains,resins, compomers, ceramers or other direct restorative materialsconventionally used in making dental prosthetics, or in repairingdiscolored, chipped, broken or malformed teeth, typically provide colormatching shade guides to dentists which illustrate the various coloredporcelains available. As shown in FIG. 1, one such shade guide 10includes a variety of shade tabs 12, each made of a different coloredporcelain available from a manufacturer. A dentist determines the colorof a patient's natural teeth by detaching individual shade tabs 12 fromthe shade guide 10 and holding the shade tabs 12 next to the patient'snatural teeth for comparison. Once a color match is found, the dentistorders a dental prosthesis from a dental laboratory in the matchingcolored porcelain or other material, or, if the patient's teeth arebeing whitened, the dentist uses the color match as a base against whichto compare the eventual results of the whitening process.

[0007] This somewhat rudimentary method often provides less thandesirable results because of the inaccuracy inherent in the dentist“eyeballing” the color match. Poor lighting, poor vision, eye fatigue,conflicting ambient colors or even lack of patient cooperation in theprocess, among other things, can cause the dentist to miss the bestmatch. More importantly, the best match is often a combination of two ormore colored porcelains, sometimes from different manufacturers, whichis difficult to discern by the human eye.

[0008] Accordingly, a variety of mechanical and electronic devices havebeen devised to aid in matching tooth shades. Some of these devices aredescribed in U.S. Pat. Nos. 5,766,006 to Murljacic, 5,759,030 to Jung etal., 5,690,486 to Zigelbaum, 5,529,492 to Yarovesky et al., 5,383,020 toVieillefosse, 5,055,040 to Clar, 4,654,794 to O'Brien, and 4,110,826 toMöllgaard. Unfortunately, none of these devices has been very successfulin advancing the tooth shade matching process much beyond the“eyeballing” procedure described above. Therefore, there exists a needin the art for an improved tooth shade matching system.

BRIEF SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, a computer-aided systemprovides apparatus and methods for capturing an image of a patient'steeth and analyzing such image with respect to the inherent toothcoloration and shading characteristics of the patient's teeth for thepurposes of reproducing such inherent coloration and shading inrestorative procedures and prosthetics.

[0010] A method for matching color of a dental prosthetic to a patient'stooth color is disclosed. The method includes acquiring an image of apatient's teeth containing normalization references and electronicallytransmitting the image to a remote location. The method may furtherincludes normalizing the electronically transmitted image using thenormalization references to obtain a normalized image and standardizingthe normalized image by matching the normalized image to selected shadestandards.

[0011] A system for matching color of a dental prosthetic to a patient'stooth color is disclosed. The system includes a computer systemconfigured for communication over a network and for receiving an imageof a patient's teeth containing normalization references and a computerprogram configured for execution on the computer system implementing amethod for matching color of a dental prosthetic. The method embodied inthe computer program may include receiving an image of a patient's teethfrom the network and analyzing colors in the image and matching thecolors to standardized colors from a selected shade standard. Thenetwork may be the Internet.

[0012] A method for manufacturing a dental prosthetic is disclosed. Themethod may include providing a computer including memory, a processorand configured for communication over a network. The method may furtherinclude receiving an image of a patient's teeth including normalizationreferences from the network, normalizing the image using thenormalization references to obtain a normalized image and standardizingthe normalized image by matching the normalized image to selected shadestandards. The method may further include assigning a pseudo-color toeach standard color in the selected shade standard, generating apseudo-color image and manufacturing said dental prosthetic using colorsidentified in said pseudo-color image.

[0013] These embodiments of the present invention will be readilyunderstood by reading the following detailed description in conjunctionwith the accompanying figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings illustrate what is currently regarded as a best modefor carrying out the invention. Additionally, like reference numeralsrefer to like parts in different views or embodiments of the drawings.

[0015]FIG. 1 is a side view of a conventional shade guide.

[0016]FIG. 2A is a flow diagram illustrating a prosthetic toothmanufacturing method of this invention.

[0017]FIG. 2B is a block diagram illustrating an electronic systemimplementing the prosthetic tooth manufacturing method of FIG. 2A.

[0018]FIG. 3 is a flow diagram illustrating in more detail a patientimage analysis procedure of the prosthetic tooth manufacturing method ofFIG. 2A.

[0019]FIG. 4 is a screen capture illustrating a thumbnail gallerypatient image display step and a patient image selection step of thepatient image analysis procedure of FIG. 3.

[0020]FIGS. 5A, 5B, and 5C are screen captures illustrating a patientimage normalization step of the patient image analysis procedure of FIG.3.

[0021] FIGS. 6 is a screen capture illustrating a standards selectionstep of the patient image analysis procedure of FIG. 3.

[0022]FIGS. 7A and 7B are screen captures illustrating a standardizationsensitivity selection step and a standardization step of the patientimage analysis procedure of FIG. 3.

[0023]FIG. 8 is a screen capture illustrating a pseudo-color mappingstep of the patient image analysis procedure of FIG. 3.

[0024]FIG. 9 is a screen capture illustrating a quality analysis step ofthe prosthetic tooth manufacturing method of FIG. 2A.

[0025]FIG. 10 is a diagram illustrating a computer-readable storagemedium storing software implementing the prosthetic tooth manufacturingmethod of FIG. 2A.

DETAILED DESCRIPTION OF THE INVENTION

[0026] As shown in FIG. 2A, a method 20 for manufacturing a prosthetictooth in accordance with this invention begins with a dentist acquiringdigital images of a patient's natural teeth. It should be noted thatalthough this invention will be described with respect to themanufacturing of a prosthetic tooth or teeth, those having skill in thetechnical field of this invention will understand that the invention isapplicable to manufacturing a wide variety of other dental prostheticsincluding, for example, crowns, bridges, removable dentures and veneers.Further, the invention described herein may be used for restoring apatient's natural teeth when, for example, a tooth becomes broken,chipped or modified from its original condition, thereby requiring someform of restoration, such as bonding or filling. It will also beunderstood that while a dentist will typically acquire the patientimages, others may do so instead including, for example, a dentalhygienist, assistant, or technician. Further, it will be understood thatin some circumstances the “natural” teeth in the acquired images mayactually include previously installed dental prosthetics.

[0027] As shown in FIG. 2B, the method 20 (FIG. 2A) is implemented, inpart, in software executing in an electronic system 22 comprising aninput device 24, an output device 26, a processor device 28, and amemory device 30. The software may preferably be a Windows 95®- orWindows 98®-compatible, 32-bit stand-alone application, but may insteadbe compatible with any other operating system or environment including,for example, UNIX, LINUX, the Apple OS, Windows® 3.x, and DOS. Also, thesoftware may include, or be compliant with, ActiveX controls or JavaApplets. The electronic system 22 is preferably an IBM-PC-compatiblecomputer system, but may instead comprise any other computer orelectronic system.

[0028] The dentist acquires the patient teeth images using the inputdevice 24, which may be any suitable device for acquiring digital imagesincluding, for example: a standard or intra-oral analog color ChargeCoupled Device (CCD) video camera providing a video feed to aTWAIN-compliant frame capture PC-card; a digital camera providingdigital images directly to a 32-bit TWAIN driver through a SCSI port;and a color image scanner scanning photographic slides, pictures, andthe like and providing the resulting digital images directly to a 32-bitTWAIN driver through a SCSI port. Of course, the patient images may havepreviously been acquired and stored on a storage medium, such as a Jazz®or Zip® disc, in which case the dentist may “reacquire” them bytransferring them from the storage medium to the electronic system 22.

[0029] In order to reduce shade variation in the patient images due tothe camera angle at which the images are taken, it is preferable, butnot necessary, that the dentist use standardized camera angles. Forexample, the dentist may take standard left, right, and straight-onpictures level with the patient's mouth. Of course, other standardizedangles are also possible or helpful, such as inferior and superiorangles.

[0030] Also, in order to reduce variations due to camera type, lightingconditions, etc., the dentist inserts black and white reference tabsinto the images to provide references with respect to which the imagesmay be normalized, as will be described in more detail below withrespect to FIGS. 5A, 5B, and 5C. These black and white reference tabsare manufactured using homogeneous, non-reflective porcelains, and areintended to define the respective minimum and maximum Red, Green, andBlue (RGB) values for each image.

[0031] Referring once again to FIG. 2A, after acquiring the patientimages, the dentist sends the images to a dental laboratory for analysisby a lab technician. Of course, it should be understood that while thisinvention will be described in the context of a dentist taking thepictures and installing the prosthetic tooth and a lab technicianperforming the image analysis and manufacturing the prosthetic tooth,other arrangements are possible. For example, the dentist might performthe image analysis and send the analyzed images to the dentaltechnician, or the patient's images may be taken at the dentallaboratory by the lab technician. Also, although the description hereinimplies a degree of physical distance between the dentist's office andthe dental laboratory, the dentist and the laboratory may, in fact,reside in close physical proximity, including within the same offices.Thus, the dentist and the lab technician may use the same computersystem if they are located in the same offices, thereby eliminating theneed for the dentist to “send” the images to the lab technician.

[0032] The dentist may send the patient images to a dental laboratoryusing a wide variety of means including, for example, an e-mail, anInternet download, a modem-to-modem download, and delivery of a storagemedium, such as a Jazz® or Zip® disc, on which the images are stored.

[0033] Upon receiving the patient images, the lab technician analyzesthe images using another electronic system 22 (FIG. 2B) adapted usingsoftware for his or her use in implementing another part of the method20. As described herein, the dentist and the lab technician have nearlyidentical software executing on their respective electronic systems 22(FIG. 2B). However, it will be understood that certain functionsdesirable in the lab technician's software (e.g., image analysis) maynot be necessary to the dentist's software (and therefore may not bepresent therein), and vice-versa.

[0034] As shown in FIGS. 3 and 4, the lab technician begins analysis ofthe images by displaying them in a thumbnail gallery 40. The labtechnician then selects one of the images from the gallery 40 foranalysis, and displays the selected image 42 in large format.

[0035] As shown in FIGS. 3, 5A and 5B, the lab technician continues theimage analysis procedure by normalizing the selected image 42. The labtechnician begins the normalization process by selecting a “Set BlackReference” button 50, and then adjusting and moving a selection area 52so it identifies a black reference tab 54 previously inserted into theselected image 42 by the dentist. With the black reference tab 54identified, the software executing on the lab technician's system 22(FIG. 2B) then determines the Black Reference RGB value by determiningthe average red, green, and blue values among all the pixels in theselection area 52. A similar procedure involving a “Set White Reference”button 56, the selection area 52, and a white reference tab 58 allow forthe determination of the average red, green, and blue values for a WhiteReference RGB value as well. The Black and White References may begenerally referred to as “normalization references.”

[0036] With the Black and White Reference RGB values determined, thesoftware then calculates a normalized look-up table for the selectedimage 42. An example may help explain this aspect of the disclosure.Assume, for the moment, that each pixel of the selected image 42 isstored as an 8-bit index into a 256 color look-up table such as thefollowing: TABLE 1 Index Red Green Blue 00000000 00000010 0000010100000001 00000001 00000100 00000110 00000011 00000010 00000101 0000011100000101 ... ... ... ... 11111110 11110110 11111101 11111100 1111111111111001 11111110 11111111

[0037] Under this circumstance, the software normalizes the look-uptable by recalculating the red, green and blue values for each index.The calculations are as follows:

New Red Value=(255÷Red Range)×(Index−Black Reference Red Value)+0.5  (1)

New Green Value=(255÷Green Range)×(Index−Black Reference GreenValue)+0.5   (2)

New Blue Value=(255÷Blue Range)×(Index−Black Reference Blue Value)+0.5  (3)

[0038] where,

Red Range=White Reference Red Value−Black Reference Red Value   (4)

Green Range=White Reference Green Value−Black Reference Green Value  (5)

Blue Range=White Reference Blue Value−Black Reference Blue Value   (6)

[0039] Of course, images that directly store the red, green, and bluevalues for each pixel (e.g., so-called “24-bit” images), and that,therefore, do not use a look-up table, may be normalized in much thesame way, except that the normalization procedure is performed on thepixel values of the image itself rather than on the values in a look-uptable.

[0040] Continuing with the example described above, once the look-uptable for the selected image 42 is normalized, the selected image 42 isredisplayed as a normalized image 60, as shown in FIG. 5C, using thenormalized look-up table.

[0041] As shown in FIGS. 3 and 6, with the selected image 42 (FIG. 5A)normalized, the lab technician may then select the shade standards 62 tobe used in manufacturing the prosthetic tooth. Although the shadestandards can be generated from images of the conventional shade guidespreviously described, it is preferable that the shade standards begenerated from flat, non-reflective, homogeneous porcelain samples. Thisis because the conventional shade guides are manufactured to look like aconventional tooth, and thus are curved, semi-glossy, andnon-homogeneous in the porcelain shade they represent. Thus, forexample, a conventional shade standard “a-1” shade tab is made to looklike a tooth, so it is curved, semi-glossy, and is only a true “a-1”porcelain in its center. The preferred flat, non-reflective, homogeneousporcelain samples are better adapted to provide accurate shade standardsfor digital image analysis.

[0042] As shown in FIGS. 3, 7A, and 7B, with the shade standardsselected, the lab technician then selects a standardization sensitivitylevel using a sensitivity selector 64, and the software then attempts tomatch each pixel in the normalized image 60 (FIG. 5C) to one of theselected standards. To accomplish this for each pixel, the softwarecalculates a “distance” between the RGB values of the pixel and the RGBvalues of each of the selected standards, according to the followingequation:

distance=(R _(pixel) −R _(standard))²+(G _(pixel) −G _(standard))²+(B_(pixel) −B _(standard))²  (7)

[0043] The software then determines the standard having the minimumdistance calculated. If this minimum distance does not exceed thesensitivity level (e.g., 4,000) set by the lab technician, the softwaredetermines that the standard with the minimum distance matches the pixeland assigns this standard color to the pixel. If, instead, the softwaredetermines that the minimum distance calculated exceeds the sensitivitylevel selected, then the software assigns the color black to the pixel.As shown in FIG. 7A, the software then displays a standardized image 66with the colors assigned to each pixel.

[0044] It should be noted that the standardized image 66 is displayedalongside a statistical analysis 68 of the percentage of the image 66occupied by the various standards. As shown in FIG. 7B, this statisticalanalysis 68 can also be confined to a selected region 70.

[0045] As shown in FIG. 8, pseudo-colors can be assigned to eachstandard to generate a pseudo-color image 80 in which the differencesbetween various standards is easier to discern than in the standardizedimage 66 of FIG. 7A. Thus, for example, a standard shade “a-1”, whichmay be a light tan color, may be assigned a pseudo-color of yellow,while a standard shade “a-2”, which may be a slightly darker tan color,may be assigned a pseudo-color of grass green. As a result, while thedistinctions between a-1 (light tan color) and a-2 (slightly darker tancolor) may be difficult to discern from the standardized image 70, theyreadily stand out in the pseudo-color image 80 because of thecontrasting yellow and grass green colors.

[0046] As shown in FIG. 2A, once the patient images have been analyzed,the lab technician manufactures the prosthetic tooth using thepseudo-color image 80 (FIG. 8) as a guide. As shown in FIGS. 2A and 9,the lab technician then analyzes the quality of the prosthetic tooth 90by comparing a normalized image of the prosthetic tooth 90 with thenormalized image 60 of the patient's natural tooth using the software.Specifically, the technician selects the natural tooth and theprosthetic tooth using selection regions 92 and 94, and the softwarethen calculates the average difference 96 in shades between the tworegions 92 and 94. A dentist may specify that the prosthetic tooth mustnot exceed a certain maximum average difference (e.g., 10%), and thedental laboratory may charge different fees for prosthetic teethguaranteed to fall below certain maximum average differences (e.g., $500for 2%, $300 for 5%, $150 for 10%, etc.).

[0047] Once the lab technician has confirmed that the prosthetic toothmeets the specified quality standard, the technician can send an imageof the prosthetic tooth to the dentist so the dentist can confirm thequality of the tooth using his own software in the same manner asdescribed immediately above. The dentist can then contact the patient sothat the dentist and patient can confer and agree as to theacceptability of the prosthesis. The dentist may confer in-person withthe patient or may transmit the image to the patient be electronic mailfor review and discussion. If changes are required, those can beconveyed to the lab technician for implementation into the image forfinal review before the actual prosthetic tooth is completed. Once thedentist authorizes delivery of the prosthetic tooth, the lab techniciansends the tooth to the dentist, and the dentist installs the tooth inthe patient.

[0048] It should be understood that while this invention has beendescribed with respect to a process for manufacturing a prosthetic toothor bridge or dentures, the system is equally applicable to restorationof teeth in the dentist's office when, for example, a patient's tooth isbroken, chipped or otherwise modified from its original condition, andin such instances, the dentist may prepare the image and analyze itwithin his office to determine an accurate restoration of the tooth. Thesystem of the invention is equally applicable to a process for teethwhitening. In such a process, the image analysis procedures describedherein are used to determine the shade of a patient's teeth, and then tocompare the shade of the post-whitening teeth to the shade of thepre-whitening teeth.

[0049] It should also be understood that while this invention has beendescribed with respect to colors described in the RGB format, theinvention may alternatively incorporate any other applicable format fordescribing colors including, for example, the Hue, Saturation, andLuminance (HSL) or Hue, Value and Chroma format.

[0050] As shown in FIG. 10, a computer-readable storage medium 100stores the software previously described. The storage medium 100 may be,for example, a floppy disc, a Jaz® or Zip® disc, a hard drive, a CD-ROM,a DVD-ROM, a flash EEPROM card, a magnetic tape, or a ROM, PROM, EPROM,EEPROM, or flash EEPROM chip.

[0051] Although this invention has been described with reference toparticular embodiments, the invention is not limited to these describedembodiments. For example, while the various steps and procedures of themethods of this invention have been described as occurring in aparticular order, the invention is not limited to the described order.Rather, the invention is limited only by the appended claims, whichinclude within their scope all equivalent devices or methods thatoperate according to the principles of the invention as described.

What is claimed is:
 1. A method for matching color of a dentalprosthetic to a patient's tooth color comprising: acquiring an image ofa patient's teeth containing normalization references; electronicallytransmitting said image to a remote location; normalizing saidelectronically transmitted image using said normalization references toobtain a normalized image; and standardizing said normalized image bymatching said normalized image to selected shade standards.
 2. Themethod of claim 1, wherein said acquiring an image of a patient's teethcontaining normalization references comprises taking a photograph of thepatient's teeth using an input device selected from the group includingstandard color charge coupled device (CCD) video camera, intra-oralanalog color CCD camera, digital camera and color image scanner.
 3. Themethod of claim 1, wherein said normalization references comprise blackand white normalization references.
 4. The method of claim 1, whereinsaid electronically transmitting said image to a remote locationcomprises transmitting said image over a public Internet.
 5. The methodof claim 1, wherein said normalizing said electronically transmittedimage using said normalization references comprises adjusting a colorvalue for each pixel in said image such that all colors selectivelyrange between color extremes defined by said normalization references.6. The method of claim 1, wherein standardizing said normalized imagecomprises: selecting one of a plurality of available shade standards toobtain said selected shade standard; and matching each pixel in saidnormalized image with a standard color in said selected shade standard.7. The method of claim 6, further comprising: assigning a pseudo-colorto each standard color in said selected shade standard; and generating apseudo-color image.
 8. The method of claim 7, further comprisingmanufacturing a dental prosthetic in accordance with said standardizedimage or said pseudo-color image.
 9. A system for matching color of adental prosthetic to a patient's tooth color comprising: a computersystem configured for communication over a network and for receiving animage of a patient's teeth containing normalization references; acomputer program configured for execution on said computer systemimplementing a method for matching color of a dental prosthetic, saidmethod comprising: receiving said image of a patient's teeth from saidnetwork; and analyzing colors in said image and matching said colors tostandardized colors from a selected shade standard.
 10. The system ofclaim 9, wherein said network comprises an Internet.
 11. The system ofclaim 9, wherein said computer program configured for execution on saidcomputer system implementing said method for matching said color of saiddental prosthetic, said method further comprises normalizing saidreceived image in accordance with normalization references included insaid received image.
 12. The system of claim 11, wherein saidnormalization references comprise black and white normalizationreferences.
 13. The system of claim 9, wherein said computer programconfigured for execution on said computer system implementing saidmethod for matching said color of said dental prosthetic, said methodfurther comprises: assigning a pseudo-color to each standard color insaid selected shade standard; and generating a pseudo-color image. 14.The system of claim 13, further comprising providing a laboratory formanufacturing a dental prosthetic in accordance with said pseudo-colorimage.
 15. The system of claim 13, wherein said computer programconfigured for execution on said computer system implementing saidmethod for matching said color of said dental prosthetic, said methodfurther comprises sending said pseudo-color image to a laboratory formanufacturing said dental prosthetic.
 16. A method for manufacturing adental prosthetic, comprising: providing a computer including memory, aprocessor and configured for communication over a network; receiving animage of a patient's teeth including normalization references from saidnetwork; normalizing said image using said normalization references toobtain a normalized image; standardizing said normalized image bymatching said normalized image to selected shade standards; assigning apseudo-color to each standard color in said selected shade standard;generating a pseudo-color image; and manufacturing said dentalprosthetic using colors identified in said pseudo-color image.
 17. Themethod of claim 16, wherein said network is an Internet.
 18. The methodof claim 16, wherein said normalization references comprise black andwhite normalization references.
 19. The method of claim 16, furthercomprising sending said pseudo-color image over said network to a dentalprosthetic manufacturing laboratory.
 20. The method of claim 16, furthercomprising installing said dental prosthetic in said patient.